1. Field of the Invention
This invention relates generally to the field of oil well, gas well, water well and subterranean pollution remediation well equipment, and more particularly to a wire wrapped screen having a permeable isolation screen sections for filtering sand and undesirable solids from fluids, gases and toxic extractions at subterranean locations.
2. Brief Description of the Prior Art
Many types of screens and filtering devices or well liners are known in the art that are designed to exclude sand and other solids from fluids and gases produced from oil, gas, water and pollution remediation wells without undue restriction of the production rate of fluids or gases. Well liners are sometimes used as the sole means of filtering sand from the fluids wherein the screen openings are sized to stop the movement of the formation sand and allow continual flow of fluid into the wellbore. Gravel or other particulate matter is also used in conjunction with screens such as "gravel pack" well liners wherein the gravel or particulates are sized to restrain movement of the formation sand and the screen openings are designed to restrain the movement of the gravel or particulates to allow continual flow of fluids therethrough.
Common well liners employ a base pipe having a plurality of openings through the sidewall which is surrounded by longitudinally extending spacer bars, rods, or rings and over which a continuous wire is wrapped in a carefully spaced spiral configuration to provide a predetermined constant gap between the wire wrapping. The gap allows fluids to flow through the wire wrapping and retains the movement of particulate materials such as sand or gravel. Such a well liner is also commonly referred to as a "wire wrapped" screen.
Most "wire wrapped" well liners have the common feature of an "inner annulus" or space between the base pipe and the wire wrapping. The inner annulus is desirable because it allows free transmission of fluids that flow through the wire wrapping gaps into the apertures on the base pipe. The absence of the inner annulus would significantly restrict fluid flow rates radially into the well liner.
The inner annulus in a wire wrapped well liner causes several serious problems during installation of a gravel pack and the stimulation of a well liner or gravel packed well. Problems occur in bypassing fluid through the inner annulus as the gravel is being transported down the "outer annulus", or the gap between the well liner and the wellbore, and bypassing fluid being injected from a well liner through a gravel pack into the formation to stimulate the well or seal a portion of the wellbore.
Bridges of gravel are in part created, or enhanced, as the gravel carrying fluid flows into the inner annulus. As the gravel carrying fluid moves, an increase of gravel concentration in the fluid in the outer annulus results because the gravel is restricted from entering the wire wrapped well liner but fluid enters freely. Thus, when the gravel concentration increases beyond a critical magnitude, a bridge is formed which wedges in the outer annulus and halts further movement of gravel before the outer annulus is fully packed with gravel.
Another problem results from the fluid freely entering the inner annulus from the outer annulus during gravel packing in highly deviated wellbores. The problem is commonly referred to as "duning". In wellbores having angles of 45 degrees to 90 degrees plus from the vertical, and especially those requiring the gravel to be packed along intervals ranging from several feet to more than a thousand feet, the gravel tends to fall to the low side of the wellbore due to gravity as it is being transported by the fluid. As gravel accumulates, the fluid is diverted to the high side of the wellbore and into the well liner, thereby reducing the velocity of carrier fluid in the outer annulus and the capability of the fluid to force gravel toward the bottom end of the wellbore.
No known art tackles this problem. For example, Gruesbeck et al., U.S. Pat. No. 4,046,198, attempts to solve this problem by providing the means of inserting a wash pipe in the base pipe to reduce the ease with which fluid can flow into the pipe. Maly et al., U.S. Pat. No. 3,637,010 teaches the use of flexible baffles to restrict the flow of fluids into the base pipe. However, both teachings ignore the effect of the inner annulus between the base pipe and wire wrapped screen.
Still a further problem is that gravel bridges form above intervals where no fluid flow occurs or where the fluid flow is significantly restricted, from the outer annulus into the well liner, creating "voids" in the gravel pack, or loosely packed intervals in the vicinity of the no (low) flow area. This problem may occur at the seal sections of a selective isolation screen and/or is most likely to occur in high angle wellbores. Gravel bridges are often unstable and may slump or fall and loosen the packing arrangement of the gravel, thus reducing the effectiveness of the gravel to stop formation sand movement.
Sparlin, U.S. Pat. No. 4,771,829 teaches the use of selective isolation seals positioned in the "inner annulus" which control the flow of fluid therein. One limitation of this design is that fluid cannot flow radially through the sealed sections of the screens. This prevents fluids from being produced from the wellbore directly adjacent to an inner annulus seal directly into the well liner, and inhibits tight packing of gravel in the outer annulus in the immediate vicinity of each inner annulus seal.
Other relevant patents are noted in Sparlin U.S. Pat. No. 4,771,829.